When a signal is recorded on a magnetic record medium by the use of a magnetic head, the process of compensating a loss caused to develop in a short wavelength region while recording is taking place in order to make recording to optimum conditions over the entire spectrum of recording wavelengths is referred to as recording equalization. Also, when a signal is reproduced from the foregoing record medium, the process of compensating a loss developed in a short wavelength region in order to optimize the overall wavelength output characteristics is referred to as playback equalization. This is usually carried out by setting up the amount of compensation in the short wavelength region against the long wavelength region. Particularly, when a digital signal is recorded/reproduced, it is known that a pulse waveform having a small amount of waveform distortion is obtainable by adjusting the overall output in the shortest wavelength corresponding to the minimum recording pulse width to about --6 dB of that in the long wavelength region since there exist no phase distortion in the system. The optimum recording/playback equalization characteristics differ according to the characteristics of a record/playback head and are changeable according the extent of head wear, and also differ according to the kinds of magnetic record media employing a variety of magnetic materials and finishing processes.
However, one of the following two systems is generally employed, one being a system, in which recording/playback equalization characteristics are permanently fixed with the conditions of usage such as performance variations between heads, degrees of head wear and magnetic record media and the like taken into consideration and the other being a system, in which settings of recording/playback equalization characteristics are switched according to the kinds of magnetic record media. As far as these settings of recording/playback equalization characteristics remain within acceptable limits, no practical problems are anticipated, but if these settings exceed acceptable limits, errors occur with resulting generation of noises in the case of video/audio applications.
In order to cope with the foregoing situation, automatic methods for setting up recording/playback equalization characteristics relative to the combination between head and magnetic medium have been devised. For example, JP Heisei 1(1989)-112508 titled "Method of Automatic Recording/Playback Equalization for Magnetic Tape Recording and Its Equipment" discloses a method for setting up by selecting the conditions for recording equalization, under which non-linear distortions in amplitude/phase are minimized and SN ratios are maximized over a required frequency range, and performing playback equalization to minimize error rates under the foregoing conditions for recording equalization after taking the steps of recording on a magnetic tape a test signal with the level thereof varied, the test signal being intended for use in recording equalization and playback equalization, thereby allowing an optimum adjustment to be made to the combination of a head used in specific equipment and a specific magnetic tape. However, when a magnetic tape thus recorded with signals is reproduced with the use of other equipment, the combination between the head characteristics of the equipment used in recording and the magnetic tape characteristics is made in such a way as the combination is made between each respective end of the limits of variation and also the adjustment condition of the playback equipment shows a reversed combination, error rates increase due to a big difference between the recording characteristics and the playback characteristics, resulting in a failure in practical use. Further, among the foregoing methods is found a method, whereby, in consideration of the foregoing interchangeable playback, a test signal is prerecorded in the vertical blanking period in addition to the ordinary picture signal and playback equalization is performed by utilizing the test signal.
However, even if the countermeasure as described in the above is taken, the foregoing amount of playback equalization as determined according to the test signal may be exceeding the limits of adjustment in playback equalization on the part of playback equipment, depending on a combination between the recording equipment and the playback equipment. In this case, error rates can not be improved much, resulting in a failure in practical use.